JP7151946B1 - Wound core and method for manufacturing wound core - Google Patents

Abstract

To provide a wound iron core excellent in magnetic characteristics with small transformer core loss without using two or more kinds of materials with different magnetic characteristics. The wound core of the present invention is made of a grain-oriented electrical steel sheet, has a flat portion and a corner portion adjacent to the flat portion, the flat portion has a lap portion, and the corner portion has a bent portion. and the ratio of the length of the outer circumference to the length of the inner circumference when viewed from the side (the length of the outer circumference/the length of the inner circumference) is 1.80 or less, and the grain-oriented electrical steel sheet has a strong magnetic field. The magnetic flux density B8 is 1.84 T or more and 1.91 T or less when the height H is 800 A/m, and the core loss deterioration rate is 1.50 or less under a predetermined compressive stress.

Description

TECHNICAL FIELD The present invention relates to a wound core and a method for manufacturing the wound core, and more particularly, to a wound core for a transformer and a method for manufacturing the wound core, which are made from grain-oriented electrical steel sheets.

A grain-oriented electrical steel sheet having a crystal structure in which the <001> orientation, which is the axis of easy magnetization of iron, is highly aligned in the rolling direction of the steel sheet is particularly used as an iron core material for electric power transformers. Transformers are broadly classified into stacked core transformers and wound core transformers according to their core structure. A laminated core transformer is one in which a core is formed by stacking steel plates cut into a predetermined shape. On the other hand, a wound core transformer has a core formed by winding steel sheets. There are various requirements for transformer cores, but the most important is that the iron loss be small.

From this point of view, it is important that the grain-oriented electrical steel sheet, which is the iron core material, has a small iron loss as a characteristic required. A high magnetic flux density is also required to reduce the excitation current in the transformer and reduce copper loss. This magnetic flux density is evaluated by the magnetic flux density B8(T) at a magnetizing force of 800 A/m, and generally, the higher the degree of azimuth integration in the Goss orientation, the greater the B8. An electrical steel sheet with a high magnetic flux density generally has a small hysteresis loss and is excellent in iron loss characteristics. Also, in order to reduce iron loss, it is important to highly align the crystal orientation of the secondary recrystallized grains in the steel sheet with the Goss orientation and to reduce impurities in the steel composition.

However, there is a limit to the control of crystal orientation and the reduction of impurities. That is, magnetic domain refining techniques have been developed. For example, Patent Literature 1 and Patent Literature 2 describe a heat-resistant magnetic domain refining method in which linear grooves having a predetermined depth are formed on the surface of a steel sheet. The aforementioned Patent Document 1 describes means for forming grooves by means of gear-shaped rolls. Further, Patent Document 2 describes means for forming linear grooves on the surface of a steel sheet by etching. These means have the advantage that the magnetic domain refining effect applied to the steel sheet does not disappear even when heat treatment such as strain relief annealing when forming the wound core is performed, and can be applied to the wound core.

In order to reduce the iron loss of the transformer, it is generally considered that the iron loss (material iron loss) of the grain-oriented electrical steel sheet, which is the iron core material, should be reduced. On the other hand, iron loss in transformers is often larger than material iron loss. The value obtained by dividing the iron loss value (transformer iron loss) when an electromagnetic steel sheet is used as the core of a transformer by the iron loss value of the material obtained by the Epstein test, etc. is generally called the building factor (BF) or distraction. It is called factor (DF). That is, BF generally exceeds 1 in transformers, and if BF can be reduced, transformer iron loss can be reduced.

As a general knowledge, the factor (BF factor) that causes the transformer iron loss in the wound core transformer to increase compared to the material iron loss is the magnetic flux concentration inside the core caused by the difference in the magnetic path length, the steel plate joint The occurrence of in-plane eddy current loss in the part and the increase in iron loss due to the introduction of strain during processing have been pointed out.

The increase in iron loss due to the concentration of magnetic flux inside the core due to the difference in magnetic path length is described. In the case of the single-phase wound core shown in FIG. Magnetic flux concentrates inside the core because it is short. In general, the iron loss of a magnetic material rapidly increases in a nonlinear manner as the magnetization approaches saturation as the excitation magnetic flux density increases. Therefore, when the magnetic flux concentrates inside the core, the iron loss inside the core increases peculiarly, and as a result, the iron loss of the entire core increases.

The generation of in-plane eddy current loss at steel plate joints is described below. Generally, a wound core for a transformer is provided with a cut portion for inserting a winding. After the winding is inserted into the core from the cut portion, the steel plates are joined together by providing a lap portion. As shown in FIG. 2, in the lapped portion (lapped portion) of the steel plate joint, the magnetic flux crosses the adjacent steel plate in the direction perpendicular to the plane, so an in-plane eddy current is generated. Therefore, the iron loss will increase locally.

The introduction of strain during working also causes an increase in iron loss. If strain is introduced by slitting the steel sheet, bending during core processing, or the like, the magnetic properties of the steel sheet deteriorate, and the iron loss of the transformer increases. In the case of a wound core, it is common to perform so-called strain relief annealing, in which annealing is performed at a temperature higher than the temperature at which strain is released after processing the core.

Based on these factors for increasing transformer iron loss, the following proposals have been made as measures for reducing transformer iron loss.

In Patent Document 3, an electromagnetic steel sheet having magnetic properties inferior to those on the outer peripheral side of the core is placed on the inner peripheral side of the core where the magnetic path length is short, and an electromagnetic steel sheet having magnetic properties superior to those on the inner peripheral side of the core on the outer peripheral side of the core where the magnetic path length is long. It is disclosed that by arranging the magnetic steel sheets, the concentration of the magnetic flux to the inner peripheral side of the iron core is avoided, and the iron loss of the transformer is effectively reduced. Patent Document 4 discloses an iron core design method that reduces transformer iron loss by controlling the concentration of magnetic flux and the resulting deterioration of iron loss by combining multiple types of magnetic steel sheets with different magnetic permeability and iron loss. .

Japanese Patent Publication No. 62-53579 Japanese Patent No. 2895670 Japanese Patent No. 5286292 JP 2006-185999 A

As disclosed in Patent Documents 3 and 4, in order to avoid the concentration of magnetic flux on the inner circumference side of the iron core, different materials are used on the inner circumference side and the outer circumference side of the iron core, so that the transformer characteristics are efficiently improved. can be improved. However, in these methods, it is necessary to appropriately arrange two types of materials (materials) having different magnetic properties (iron loss), which complicates the design of the transformer and significantly lowers the manufacturability.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a wound core with excellent magnetic properties and low transformer core loss without using two or more materials with different magnetic properties, and a method for manufacturing the same.

In order to obtain a wound core with excellent magnetic properties and low transformer core loss, it is necessary to select a core design that alleviates the concentration of magnetic flux and a core material that can suppress the increase in core loss even if magnetic flux concentrates inside the core. is required.

The following three points are necessary for iron core design for alleviating the concentration of magnetic flux.
(1) A wound core having a flat portion and a corner portion adjacent to the flat portion, a wrap portion on the flat portion, and a bent portion on the corner portion. Use a grain-oriented electrical steel sheet with a magnetic flux density B8 of 1.91 T or less when the strength H is 800 A/m. perimeter) is 1.80 or less

In addition, the following points are necessary for selecting core materials that can suppress the increase in core loss even if magnetic flux concentrates inside the core.
(4) Using a grain-oriented electrical steel sheet with a magnetic flux density B8 of 1.84 T or more when the magnetic field strength H is 800 A / m (5) The iron loss deterioration rate under compressive stress obtained by the following formula is Iron loss deterioration rate under compressive stress = (iron loss at compressive stress of 5 MPa) / (iron loss without compressive stress)
Here, the iron loss at a compressive stress of 5 MPa and the iron loss when there is no compressive stress in the above formula are iron losses (W / kg) measured under the conditions of a frequency of 50 Hz and a maximum magnetization of 1.7 T, and , the iron loss at a compressive stress of 5 MPa is the iron loss measured at a compressive stress of 5 MPa in the rolling direction of the iron core material.

Each requirement and reason is explained in detail.

(1) A wound core having a flat portion and a corner portion adjacent to the flat portion, a wrap portion on the flat portion, and a bent portion on the corner portion. of magnetic material is wound to form a core. In general, a method is adopted in which a steel sheet is wound into a cylinder, then pressed so that the corners thereof have a certain curvature, and formed into a rectangular shape. On the other hand, as another manufacturing method, there is a method in which the corner portions of the wound core are bent in advance, and the bent steel plates are overlapped to form the wound core. The iron core formed by this method has bent portions (bending portions) at the corner portions. An iron core formed by the former method is generally called a tranco core, and an iron core formed by the latter method is generally called a uni-core or a duo-core depending on the number of steel plate joints provided. In order to alleviate the concentration of magnetic flux, a structure in which a bent portion is provided at the corner formed by the latter method is suitable.

The results of an experimental investigation of the concentration of magnetic flux in the iron cores of the trunk core and the uni-core are shown below. A grain-oriented electrical steel sheet (magnetic flux density B8: 1.89 T, W17/50: 0.86 W/kg) with a thickness of 0.23 mm having one single-phase trunk core and two uni-cores having the shape shown in FIG. They were wound and shaped, and strain relief annealing was performed on one of the Truncco core and Unicore under the same conditions. A wound core was produced by winding 50 turns and performing no-load excitation at a magnetic flux density of 1.5 T and a frequency of 60 Hz. A one-turn search coil was arranged at the position shown in FIG. 4, and the magnetic flux density distribution in the iron core was investigated. FIG. 5 shows the maximum values of the magnetic flux densities of the iron cores of each quarter thickness from the inner winding (inner side) to the outer winding (outer side). It can be seen that both the tranco core (with strain relief annealing) and the unicore (with strain relief annealing and without strain relief annealing) have a higher magnetic flux density in the inner winding, and the concentration of magnetic flux occurs. Comparing the tranco core and the unicore, it was found that the unicore had less magnetic flux concentration.

The reason why the concentration of the magnetic flux is alleviated by the uni-core, that is, by providing the bent portion at the corner portion is presumed as follows. Deformation twins and the like remain in the bent portion of the uni-core even after the strain relief annealing, and the magnetic permeability is locally reduced compared to other portions. If such a portion with extremely low magnetic permeability exists, magnetic flux above a certain level cannot pass through. Therefore, even if there is a magnetic path length difference, it is difficult for the magnetic flux to concentrate only inside the iron core. That is, it is presumed that the concentration of magnetic flux does not occur in the inner winding portion of the uni-core compared to the truncated core which has a small magnetic permeability and does not have a bent portion.

(2) As the iron core material, use a grain-oriented electrical steel sheet having a magnetic flux density B8 of 1.91 T or less when the magnetic field strength H is 800 A / m. The result of having investigated the influence of magnetic flux density B8 is shown. A single-phase unicore having the shape shown in FIG. A winding of 50 turns was applied, and no-load excitation was performed at a magnetic flux density of 1.5 T and a frequency of 60 Hz. A one-turn search coil was arranged at the position shown in FIG. 4, and the magnetic flux density distribution in the iron core was investigated. FIG. 6 shows the maximum values of the magnetic flux densities of the iron cores of each 1/4 thickness from the inner winding to the outer winding in the unicores produced from each material (grain-oriented electrical steel sheet). As a result, the smaller the magnetic flux density B8 of the grain-oriented electrical steel sheet as the raw material, the more the concentration of the magnetic flux tends to be relaxed, but this tendency is saturated at 1.91 T or less.

The reason why the concentration of the magnetic flux in the iron core is reduced as the magnetic flux density B8 of the grain-oriented electrical steel sheet as the raw material is reduced is presumed as follows. If the magnetic flux density B8 of the iron core material is large, generally a large amount of magnetic flux can pass. When the magnetic flux density B8 of the iron core material is large, it is considered that magnetic flux concentration tends to occur inside the iron core due to the magnetic path length difference. Conversely, if the magnetic flux density B8 of the iron core material is small, the magnetic flux can only pass through to a certain extent. Therefore, even if there is a magnetic path length difference, it is difficult for the magnetic flux to concentrate only inside the iron core. In other words, when the magnetic flux density B8 of the iron core material is low, it is estimated that the concentration of the magnetic flux in the iron core is alleviated compared to when the magnetic flux density B8 is high.

(3) The ratio of the length of the outer circumference to the length of the inner circumference of the iron core (the length of the outer circumference/the length of the inner circumference) is 1.80 or less. shows the results of investigating the effect of on magnetic flux concentration. In the shape shown in FIG. 7 and Table 2, the iron core with a 0.23 mm thickness grain-oriented electrical steel sheet (magnetic flux density B8: 1.89 T, W17/50: 0 .86 W/kg). A winding of 50 turns was applied, and no-load excitation was performed at a magnetic flux density of 1.5 T and a frequency of 60 Hz. A one-turn search coil was arranged at the position shown in FIG. 4, and the magnetic flux density distribution in the iron core was investigated. The magnetic flux density increases from the outer winding to the inner winding. defined as the concentration of FIG. 8 shows the relationship between the ratio of the length of the outer circumference to the length of the inner circumference (the length of the outer circumference/the length of the inner circumference) and the concentration of the magnetic flux inside the core in each core shape. The smaller the ratio of the length of the outer circumference to the length of the inner circumference, the smaller the magnetic path length difference between the inner and outer sides of the iron core. In particular, when the ratio of the length of the outer circumference to the length of the inner circumference was 1.80 or less, the concentration of the magnetic flux inside the core was small.
In Table 2, the length of the inner circumference was calculated by 2(c+d)+4f×(√2−2). Also, the length of the perimeter was calculated by 2(a+b)+4e×(√2−2). Moreover, a and b were calculated by a=c+2w and b=d+2w, respectively.
The length of the inner circumference and the length of the outer circumference may be calculated from the length of each location as shown in Table 2, or the length of the inner circumference and the length of the outer circumference may be measured.

Next, the conditions and reasons for selecting the iron core material for suppressing the increase in iron loss when the magnetic flux is concentrated inside the iron core will be explained.

(4) Use a grain-oriented electrical steel sheet with a magnetic flux density B8 of 1.84 T or more when the magnetic field strength H is 800 A/m increases nonlinearly and rapidly as it approaches . Therefore, as described above, when the magnetic flux concentrates inside the iron core and the local magnetic flux density increases, the iron loss becomes larger than in the case of a uniform magnetic flux density distribution. From the viewpoint of saturation magnetization, the larger the saturation magnetization, the more the nonlinear increase in iron loss can be suppressed, so the increase in iron loss can be suppressed. The saturation magnetization of an electrical steel sheet is determined mainly by the amount of Si, but the magnetic flux density B8 of the iron core material is effective in increasing iron loss in the practical excitation magnetic flux density region. The results of experimentally investigating the influence of the magnetic flux density B8 of the iron core material on the iron loss of the unicore are shown. A single-phase unicore having the shape shown in FIG. A winding of 50 turns was applied, and no-load excitation was performed with a magnetic flux density of 1.5 T and a frequency of 60 Hz, and iron loss was measured. The results are shown in FIG. Iron loss was reduced in the region where the magnetic flux density B8 of the grain-oriented electrical steel sheet as the material was 1.84 T or more and 1.91 T or less. It is presumed that the iron loss is reduced in the above range due to the effect of alleviating magnetic flux concentration due to the low B8 and the effect of reducing the increase in iron loss due to the high B8.

(5) Use a grain-oriented electrical steel sheet with an iron loss deterioration rate of 1.50 or less under compressive stress. . In general, when the strain remains, the magnetic domain structure of the portion is disturbed, the magnetic permeability is deteriorated, and the iron loss of the entire iron core is deteriorated. Also, when strain relief annealing is performed after working, twin crystals are present in the rectangular bent portions, and as with residual strain, the magnetic domain structure of these portions is disturbed, the magnetic permeability is deteriorated, and the iron loss of the entire core is reduced. deteriorates. That is, if an increase in iron loss due to residual strain or twinning is suppressed, an increase in iron loss can be suppressed even when magnetic flux is concentrated inside the iron core.

We searched for a core material that can suppress the increase in iron loss due to residual strain and twinning. It turns out that it can be made smaller.

Experimental results that serve as the grounds for the preferred range are shown below. A single-phase unicore having the shape shown in FIG. Materials with different iron loss deterioration rates under compressive stress (grain-oriented electrical steel sheets A to K) were produced by changing the coating tension of the insulating coating formed on the surface of the electrical steel sheet. Iron loss deterioration rate under compressive stress decreased with increasing coating tension. The manufactured unicore was wound with 50 turns, subjected to no-load excitation at a magnetic flux density of 1.5 T and a frequency of 60 Hz, and iron loss was measured. FIG. 10 shows the relationship between the iron loss deterioration rate under compressive stress of the grain-oriented electrical steel sheet as the material and the transformer iron loss. The transformer core loss decreased in the region where the core loss deterioration rate under compressive stress was 1.50 or less.

Iron loss deterioration due to magnetic domain disturbance due to compressive stress and iron loss increase due to residual strain and twinning in the wound core are correlated. , it is presumed that the increase in iron loss can be suppressed even when the magnetic flux is concentrated inside the iron core.

The present invention has been made based on the above findings, and has the following configurations.
[1] A wound core made of a grain-oriented electrical steel sheet,
The wound core has a flat portion and a corner portion adjacent to the flat portion, the flat portion has a lap portion, the corner portion has a bent portion, and the wound core is viewed from the side. The ratio of the length of the outer circumference to the length of the inner circumference (length of the outer circumference / length of the inner circumference) is 1.80 or less,
The grain-oriented electrical steel sheet has a magnetic flux density B8 of 1.84 T or more and 1.91 T or less when the magnetic field strength H is 800 A / m, and the iron loss deterioration rate under compressive stress obtained by the following formula is 1.50 or less.
Iron loss deterioration rate under compressive stress = (iron loss at compressive stress of 5 MPa) / (iron loss without compressive stress)
Here, the iron loss at a compressive stress of 5 MPa and the iron loss when there is no compressive stress in the above formula are iron losses (W / kg) measured under the conditions of a frequency of 50 Hz and a maximum magnetization of 1.7 T, and , the iron loss at a compressive stress of 5 MPa is the iron loss measured at a compressive stress of 5 MPa in the rolling direction of the grain-oriented electrical steel sheet.
[2] The wound core according to [1], wherein the grain-oriented electrical steel sheet is subjected to heat-resistant magnetic domain refining treatment.
[3] Manufacture of a wound core made of a grain-oriented electrical steel sheet, having a plane portion and a corner portion adjacent to the plane portion, having a lap portion at the plane portion, and having a bent portion at the corner portion a method,
The ratio of the length of the outer periphery of the wound core to the length of the inner periphery (length of the outer periphery / length of the inner periphery) when viewed from the side of the wound core is 1.80 or less,
The grain-oriented electrical steel sheet has a magnetic flux density B8 of 1.84 T or more and 1.91 T or less when the magnetic field strength H is 800 A / m, and the iron loss deterioration rate under compressive stress obtained by the following formula A method for manufacturing a wound core using a grain-oriented electrical steel sheet having a is 1.50 or less.
Iron loss deterioration rate under compressive stress = (iron loss at compressive stress of 5 MPa) / (iron loss without compressive stress)
Here, the iron loss at a compressive stress of 5 MPa and the iron loss when there is no compressive stress in the above formula are iron losses (W / kg) measured under the conditions of a frequency of 50 Hz and a maximum magnetization of 1.7 T, and , the iron loss at a compressive stress of 5 MPa is the iron loss measured at a compressive stress of 5 MPa in the rolling direction of the grain-oriented electrical steel sheet.
[4] The method for manufacturing a wound core according to [3], wherein the grain-oriented electrical steel sheet is subjected to heat-resistant magnetic domain refining treatment.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a wound core with excellent magnetic properties and low transformer core loss, and a method for manufacturing the same. According to the present invention, it is possible to obtain a wound core excellent in magnetic properties with small transformer iron loss without using two or more kinds of materials having different magnetic properties (iron loss).
According to the present invention, the complexity of iron core design such as arrangement of materials required when two or more kinds of materials having different magnetic properties are used is reduced, and a wound core excellent in magnetic properties with small iron loss is provided. It can be obtained with high manufacturability.

FIG. 1 is a schematic diagram illustrating a magnetic path inside the core and a magnetic path outside the core of a wound core. FIG. 2 is a schematic diagram illustrating crossing of magnetic flux in the direction perpendicular to the plane of a steel plate at a steel plate joint. FIG. 3 is an explanatory view (side view) for explaining the shapes of experimentally produced trancocores and unicores. FIG. 4 is an explanatory diagram for explaining the arrangement of the search coils when examining the magnetic flux density distribution in the iron core. FIG. 5 is a diagram showing the results of an investigation on the magnetic flux concentration in the iron cores of the tranco core and the unicore. FIG. 6 is a diagram showing the result of investigating the influence of the magnetic flux density B8 of the iron core material on the magnetic flux concentration in the iron core of the uni-core. FIG. 7 is an explanatory diagram (side view) explaining the shape of an experimentally produced iron core. FIG. 8 is a diagram showing the relationship between the ratio of the length of the outer circumference to the length of the inner circumference in each iron core shape and the concentration of the magnetic flux inside the iron core. FIG. 9 is a diagram showing the results of investigating the influence of the magnetic flux density B8 of the iron core material on the iron loss of the unicore. FIG. 10 is a diagram showing the relationship between the iron loss deterioration rate under compressive stress of the iron core material and the transformer iron loss. FIG. 11 is an explanatory view (side view) for explaining the shape of the trunk core produced in the example. FIG. 12 is an explanatory view (side view) explaining the shape of the unicore produced in the example.

The details of the present invention are described below.

<Wound iron core>
As described above, the following conditions must be satisfied in order to achieve a transformer wound core with low iron loss.
(A) A wound core having a flat portion and a corner portion adjacent to the flat portion, a wrap portion on the flat portion, and a bent portion on the corner portion; The length ratio of the inner circumference is 1.80 or less

(A) is satisfied by selecting a wound core manufacturing method generally called a uni-core or duo-core type. A known method can be adopted as a method for manufacturing the wound core. More specifically, when using a Unicore manufacturing machine manufactured by AEM, when the design size is read into the manufacturing machine, the steel plate is sheared to the size according to the design drawing, and the processed steel plate with bent parts is processed one by one. Since it is produced, the wound core can be produced by laminating the processed steel plates.

In the condition (B), the outer circumference and inner circumference of the core refer to the outer circumference and inner circumference of the core, respectively, when the core is viewed from the side. That is, the length of the outer circumference of the iron core is measured along the outside (outer surface) of the outermost grain-oriented electrical steel sheet (raw material) of the grain-oriented electrical steel sheets (materials) that make up the wound core when the core is viewed from the side. It is the length of one turn in the winding direction of the grain-oriented electrical steel sheet, and the length of the inner circumference of the iron core is the inner side of the innermost grain-oriented electrical steel sheet among the grain-oriented electrical steel sheets that constitute the wound core. It is the length of one turn along the (inner surface) in the winding direction of the grain-oriented electrical steel sheet. The upper limit of the ratio of the length of the outer circumference to the length of the inner circumference of the iron core needs to be 1.80. The ratio is preferably 1.70 or less, more preferably 1.60 or less. Although the lower limit of the ratio is not specified in terms of characteristics, it is determined by the relationship between the core size and the thickness because the core thickness decreases when the ratio approaches 1. As an example, the lower limit of said ratio is 1.05.

If the above requirements (A) and (B) are controlled within the scope of the present invention, other than (A) and (B), the type of steel plate joints, the core size, the bending angle of the bent portion, the number of bent portions, etc. Not limited.

<Grain-oriented electrical steel sheet constituting wound core>
As described above, the following conditions must be satisfied in order to achieve a transformer wound core with low iron loss.

(C) As the iron core material, a grain-oriented electrical steel sheet having a magnetic flux density B8 of 1.84 T or more and 1.91 T or less when the magnetic field strength H is 800 A / m is used. Magnetic properties are measured by the Epstein test. . The Epstein test is carried out by a known method such as IEC standards or JIS standards. Alternatively, when it is difficult to evaluate the magnetic flux density B8 by the Epstein test, such as a non-heat-resistant magnetic domain refining material, the result of the single plate magnetic measurement test (SST) may be substituted. When selecting the suitable range of magnetic flux density B8 for wound core production, typical characteristics of grain-oriented electrical steel sheet coils should be used. Specifically, a test sample is taken from the tip and tail ends of the steel sheet coil, the Epstein test is performed, the magnetic flux density B8 is measured, and the average value is adopted as the representative characteristic. Alternatively, materials may be selected based on the characteristic values (average values and guaranteed values) of steel sheets provided by steel material manufacturers. The magnetic flux density B8 is preferably 1.86 T or more.

(D) As the core material, use a grain-oriented electrical steel sheet whose iron loss deterioration rate under compressive stress obtained by the following formula is 1.50 or less Iron loss deterioration rate under compressive stress = (at a compressive stress of 5 MPa iron loss) / (iron loss without compressive stress)
The iron loss at a compressive stress of 5 MPa and the iron loss without compressive stress, defined in the above formula, are measured with the same single plate magnetic measuring device under the conditions of a frequency of 50 Hz and a maximum magnetization of 1.7 T. The iron loss is (W/kg), and the iron loss at a compressive stress of 5 MPa is the iron loss measured at a compressive stress of 5 MPa in the rolling direction of the grain-oriented electrical steel sheet serving as the core material. Compressive stress is applied to the compression side at 5 MPa uniaxially in the rolling direction of the steel plate. Although the method of applying the compressive stress is not particularly specified, for example, there is a method of fixing one side of the steel plate with a clamp or the like and applying stress from the opposite side with a pusher or the like. At that time, it is necessary to uniformly apply stress along the rolling direction so that the steel plate does not buckle. Moreover, in order to prevent buckling, the steel plate may be fixed vertically in the vertical direction within a range that does not hinder the measurement. The iron loss in the absence of compressive stress is the iron loss measured without application of compressive stress. In the present invention, as described above, a grain-oriented electrical steel sheet having a core loss deterioration rate of 1.50 or less under the compressive stress is used as the core material. The iron loss deterioration rate under the compressive stress is preferably 1.45 or less. Although the lower limit of the iron loss deterioration rate under the compressive stress is not particularly limited, as an example, the lower limit of the iron loss deterioration rate under the compressive stress is 1.05.

As long as the requirements (C) and (D) are controlled within the scope of the present invention, the properties of the grain-oriented electrical steel sheet other than (C) and (D), the composition, the manufacturing method, etc. are not particularly limited. .

The composition and manufacturing method of the grain-oriented electrical steel sheet suitable as the raw material for the wound core of the present invention are described below.

[Component composition]
In the present invention, the chemical composition of the grain-oriented electrical steel sheet slab may be any chemical composition that causes secondary recrystallization. Further, when using an inhibitor, for example, when using an AlN-based inhibitor, Al and N are used, and when using an MnS/MnSe-based inhibitor, appropriate amounts of Mn and Se and/or S are included. good. Of course, both inhibitors may be used together. In this case, the preferable contents of Al, N, S and Se are respectively Al: 0.010 to 0.065% by mass, N: 0.0050 to 0.0120% by mass, S: 0.005 to 0.030 % by mass, Se: 0.005 to 0.030% by mass.

Furthermore, the present invention can also be applied to grain-oriented electrical steel sheets with limited Al, N, S, and Se contents and no inhibitors. In this case, the amounts of Al, N, S and Se are preferably suppressed to Al: 100 mass ppm or less, N: 50 mass ppm or less, S: 50 mass ppm or less, and Se: 50 mass ppm or less.

The basic components and optional additive components of the grain-oriented electrical steel sheet slab are specifically described below.

C: 0.08% by mass or less C is added to improve the texture of the hot-rolled sheet. However, if the C content exceeds 0.08% by mass, it becomes difficult to reduce the C content to 50 ppm by mass or less at which magnetic aging does not occur during the manufacturing process, so the C content is 0.08% by mass or less. It is preferable to Regarding the lower limit of the C content, it is not particularly necessary to set a lower limit because secondary recrystallization is possible even with a material that does not contain C. That is, the C content may be 0% by mass.

Si: 2.0 to 8.0% by mass
Si is an element effective in increasing the electric resistance of steel and improving iron loss. When the Si content is 2.0% by mass or more, a sufficient iron loss reduction effect can be obtained more easily. On the other hand, when the Si content is 8.0% by mass or less, significant deterioration in workability can be suppressed, and a decrease in magnetic flux density can be easily suppressed. Therefore, the Si content is preferably in the range of 2.0 to 8.0% by mass.

Mn: 0.005 to 1.000% by mass
Mn is an element necessary for improving hot workability. When the Mn content is 0.005% by mass or more, the effect of addition can be easily obtained. On the other hand, when the Mn content is 1.000% by mass or less, it becomes easier to suppress the decrease in the magnetic flux density of the product sheet. Therefore, the Mn content is preferably in the range of 0.005 to 1.000% by mass.

Cr: 0.02 to 0.20% by mass
Cr is an element that promotes the formation of a dense oxide film at the interface between the forsterite film and the base iron. Although it is possible to form an oxide film without adding Cr, adding 0.02% by mass or more of Cr is expected to expand the suitable range of other components. Further, when the Cr content is 0.20% by mass or less, it is possible to suppress the oxide film from becoming too thick, and it becomes easy to suppress the deterioration of the coating peeling resistance. Therefore, the Cr content is preferably in the range of 0.02 to 0.20% by mass.

It is preferable that the slab for grain-oriented electrical steel sheet has the above components as basic components. The slab can appropriately contain the following elements in addition to the above components.

Ni: 0.03 to 1.50% by mass, Sn: 0.010 to 1.500% by mass, Sb: 0.005 to 1.500% by mass, Cu: 0.02 to 0.20% by mass, P: At least one selected from 0.03 to 0.50% by mass and Mo: 0.005 to 0.100% by mass

Ni is an element useful for improving the structure of the hot-rolled sheet and improving the magnetic properties. When the Ni content is 0.03% by mass or more, the effect of improving the magnetic properties can be more easily obtained. When the Ni content is 1.50% by mass or less, it is possible to suppress the secondary recrystallization from becoming unstable, and it becomes easy to reduce the risk of deterioration of the magnetic properties of the product sheet. Therefore, when Ni is contained, the Ni content is preferably in the range of 0.03 to 1.50% by mass.

In addition, Sn, Sb, Cu, P and Mo are elements useful for improving magnetic properties, respectively, and when the content of each component is at least the lower limit of the content of each component described above, the effect of improving the magnetic properties is more likely to be obtained. . On the other hand, when the content of each component is equal to or less than the upper limit of the above-described content, it becomes easier to reduce the possibility that the growth of secondary recrystallized grains is inhibited. Therefore, when Sn, Sb, Cu, P, and Mo are contained, it is preferable that the content of each element is set in the above range.

The balance other than the above components is unavoidable impurities and Fe mixed in the manufacturing process.

Next, a method for manufacturing a grain-oriented electrical steel sheet suitable as a material for the wound core of the present invention will be described.

[heating]
A slab having the above component composition is heated according to a conventional method. The heating temperature is preferably 1150 to 1450°C.

[Hot rolling]
After the heating, hot rolling is performed. After casting, hot rolling may be performed immediately without heating. In the case of thin cast slabs, hot rolling may be performed, or hot rolling may be omitted. When hot rolling is carried out, it is preferable to carry out the rolling temperature of the final pass of rough rolling at 900° C. or higher and the rolling temperature of the final pass of finish rolling at 700° C. or higher.

[Hot-rolled sheet annealing]
After that, the hot-rolled sheet is annealed as necessary. At this time, the hot-rolled sheet annealing temperature is preferably in the range of 800 to 1100° C. in order to develop the Goss texture in the product sheet to a high degree. If the hot-rolled sheet annealing temperature is lower than 800°C, the band structure in the hot rolling remains, making it difficult to achieve a primary recrystallized structure with uniform grains and inhibiting the development of secondary recrystallization. There is a risk. On the other hand, if the hot-rolled sheet annealing temperature exceeds 1100° C., the grain size after the hot-rolled sheet annealing becomes too coarse, which may make it extremely difficult to achieve a uniform primary recrystallization structure.

[Cold rolling]
After that, cold rolling is performed once or twice or more with intermediate annealing. The intermediate annealing temperature is preferably 800°C or higher and 1150°C or lower. Also, the intermediate annealing time is preferably about 10 to 100 seconds.

[Decarburization annealing]
After that, decarburization annealing is performed. In the decarburization annealing, it is preferable to set the annealing temperature to 750 to 900° C., the oxidizing atmosphere PH ₂ O/PH ₂ to 0.25 to 0.60, and the annealing time to about 50 to 300 seconds.

[Application of annealing separator]
After that, an annealing separator is applied. The annealing separator preferably contains MgO as a main component and is applied in an amount of about 8 to 15 g/m ² .

[Finish annealing]
After that, finish annealing is performed for the purpose of secondary recrystallization and formation of a forsterite coating. It is preferable that the annealing temperature is 1100° C. or higher and the annealing time is 30 minutes or longer.

[Planarization and insulation coating]
After that, a flattening process (planarizing annealing) and an insulating coating are applied. It should be noted that it is also possible to perform a flattening process at the same time as applying and baking the insulating coating when applying the insulating coating to correct the shape. The flattening annealing is preferably performed at an annealing temperature of 750 to 950° C. for an annealing time of about 10 to 200 seconds. In the present invention, an insulating coating can be applied to the surface of the steel sheet before or after flattening annealing. The insulation coating here means a coating (tension coating) that applies tension to the steel sheet in order to reduce iron loss. Tensile coatings include inorganic coatings containing silica, ceramic coatings by physical vapor deposition, chemical vapor deposition, and the like.

In general, the iron loss deterioration rate under compressive stress decreases as the tensile tension applied to the steel sheet by the surface coating (forsterite coating and insulation coating) increases. In order to increase the film tension, the thickness of the tension coating may be increased, but there is concern about deterioration of the space factor. In order to obtain strong tension without deteriorating the space factor, in the case of an inorganic coating containing silica, there is a measure such as promoting glass crystallization by raising the baking temperature. Applying a film with a low coefficient of thermal expansion such as a ceramic coating is also effective in obtaining strong tension.

[Magnetic domain refining treatment]
In order to reduce the iron loss of the steel sheet, it is preferable to apply a magnetic domain refining treatment. The magnetic domain refining technology is a technology for reducing the core loss by refining the width of the magnetic domains by introducing non-uniformity to the surface of the steel sheet by a physical method. Magnetic domain refining techniques are roughly divided into heat-resistant magnetic domain refining whose effect is not impaired by strain relief annealing, and non-heat-resistant magnetic domain refining whose effect is reduced by strain relief annealing. The present invention can be applied to any of a steel sheet not subjected to magnetic domain refining treatment, a steel sheet subjected to heat-resistant magnetic domain refining treatment, and a steel sheet subjected to non-heat-resistant magnetic domain refining treatment.

Among them, steel sheets subjected to heat-resistant magnetic domain refining treatment are more suitable than steel sheets subjected to non-heat-resistant magnetic domain refining treatment. Non-heat-resistant magnetic domain refining treatment generally involves irradiating a steel sheet after secondary recrystallization with a high-energy beam (laser, etc.). This is a process for refining magnetic domains by forming a field. When compressive stress is applied to non-heat-resistant magnetic domain refining treated materials (steel sheets subjected to non-heat-resistant magnetic domain refining treatment), the stress field due to the energy beam irradiation is disturbed and the magnetic domain refining effect is reduced. The iron loss increases due to compressive stress. Therefore, a steel sheet subjected to heat-resistant magnetic domain refining treatment is more suitable. As a heat-resistant magnetic domain refining treatment method, a known technique such as forming linear grooves of a predetermined depth on the surface of the steel sheet can be applied.

The present invention will be specifically described based on examples. The following examples show preferred examples of the present invention, and the present invention is not limited by the examples. The embodiments of the present invention can be modified as appropriate within the scope of the gist of the present invention, and all of them are included in the technical scope of the present invention.

[Example 1]
11 and Tables 5, 12 and 6, and grain-oriented electrical steel sheets, which are core materials shown in Table 7, single-phase tranco-cores and uni-cores were produced. For conditions 1 to 41, after molding, strain relief annealing was performed at 800° C. for 2 hours. After annealing, the iron core was unwound from the joint and a 50-turn winding coil was inserted. Further, in conditions 42 to 47, the wound coil was inserted without performing the strain relief annealing. Then, under the conditions of excitation magnetic flux density (Bm) of 1.5 T and frequency (f) of 60 Hz, transformer iron loss was measured. Under the same conditions, the Epstein test result of the core material (in the case of non-heat-resistant magnetic domain refining, the single plate magnetic measurement result) is taken as the material iron loss, and the iron loss increase rate BF in the transformer iron loss for that material iron loss is asked. In Table 5 (in the case of tranco core), the length of the inner circumference was calculated by 2(c+d)−8f×(1−π×90(°)/360(°)). The length of the outer circumference was calculated by 2(a+b)-8e×(1-π×90(°)/360(°)). Moreover, a and b were calculated by a=c+2w and b=d+2w, respectively. The length of the inner circumference and the length of the outer circumference of the Unicore in Table 6 were calculated in the same manner as in Table 2.

Results are shown in Table 7. It was found that the suitable example and the optimum example of the present invention exhibited excellent transformer characteristics, with better BF and smaller transformer iron loss than the comparative example. In particular, the optimal example using the heat-resistant magnetic domain refining material had a particularly small transformer core loss.

Claims (4)

A wound core made of a grain-oriented electrical steel sheet,
The wound core is
A length of an outer circumference of the wound core when viewed from the side, having a flat portion and a corner portion adjacent to the flat portion, having a wrap portion on the flat portion, having a bent portion on the corner portion, and The ratio of the length of the inner circumference (length of the outer circumference/length of the inner circumference) is 1.80 or less,
The grain-oriented electrical steel sheet is
The magnetic flux density B8 is 1.84 T or more and 1.91 T or less when the magnetic field strength H is 800 A / m, and the iron loss deterioration rate under compressive stress obtained by the following formula is 1.50 or less. , wound iron core.
Iron loss deterioration rate under compressive stress = (iron loss at compressive stress of 5 MPa) / (iron loss without compressive stress)
Here, the iron loss at a compressive stress of 5 MPa and the iron loss when there is no compressive stress in the above formula are iron losses (W / kg) measured under the conditions of a frequency of 50 Hz and a maximum magnetization of 1.7 T, and , the iron loss at a compressive stress of 5 MPa is the iron loss measured at a compressive stress of 5 MPa in the rolling direction of the grain-oriented electrical steel sheet. The wound core according to claim 1, wherein the grain-oriented electrical steel sheet is subjected to heat-resistant magnetic domain refining treatment. A method for manufacturing a wound core made of a grain-oriented electrical steel sheet, having a plane portion and a corner portion adjacent to the plane portion, having a lap portion at the plane portion, and a bent portion at the corner portion. hand,
The ratio of the length of the outer periphery of the wound core to the length of the inner periphery (length of the outer periphery / length of the inner periphery) when viewed from the side of the wound core is 1.80 or less,
The grain-oriented electrical steel sheet has a magnetic flux density B8 of 1.84 T or more and 1.91 T or less when the magnetic field strength H is 800 A / m, and the iron loss deterioration rate under compressive stress obtained by the following formula A method for manufacturing a wound core using a grain-oriented electrical steel sheet having a is 1.50 or less.
Iron loss deterioration rate under compressive stress = (iron loss at compressive stress of 5 MPa) / (iron loss without compressive stress)
Here, the iron loss at a compressive stress of 5 MPa and the iron loss when there is no compressive stress in the above formula are iron losses (W / kg) measured under the conditions of a frequency of 50 Hz and a maximum magnetization of 1.7 T, and , the iron loss at a compressive stress of 5 MPa is the iron loss measured at a compressive stress of 5 MPa in the rolling direction of the grain-oriented electrical steel sheet. The method for manufacturing a wound core according to claim 3, wherein the grain-oriented electrical steel sheet is subjected to heat-resistant magnetic domain refining treatment.

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